Microwave logical decision element



March 6, 1962 1. lTZKAN ET AL 3,024, 84

MICROWAVE LOGICAL DECISION ELEMENT Filed June 23, 1959 ATTORNM UnitedStates Patent 3 024,384 MICROWAVE LOGIbAL DECISION ELEMENT IrvingItzkan, New York, and Paul R. Mclsaae, Huntington, N.Y., assignors toSperry Rand Corporation, Great Neck, N.Y., a corporation of DelawareFiled June 23, 1959, Ser. No. 822,249 3 Claims. ((11. 3153.6)

The present invention generally relates to logical decision elementssuitable for use in computer configurations and, more particularly, tosuch an element adapted for response to input signals of extremely shorttime duration.

The operation of presently available high speed digital computers islimitedby the maximum response rate of its constituent logical elements.The minimum realizable response period now is of the order of somethingless than one microsecond. The attainment of a very substantial decreasein such a response period would open up new horizons of computation.Computers capable of solving extremely complex problems in a reasonablelength of time would then be feasible. This would permit the computationof solutions to problems which cannot now be undertaken because of theprohibitively long waiting time involved. The present inventioncontemplates a new category of logical decision devices which overcomesthe response limitations of prior art devices through the utilization ofmicrowave components and techniques.

It is the principal object of the present invention to provide a logicaldecision element suitable for use in computer configurations and adaptedfor operation in an extremely short time interval.

Another object is to provide a high speed switching device whichutilizes one input microwave signal to inhibit the amplification of asecond input microwave signal.

A further object is to produce a microwave frequency device forperforming a basic logical function over a broad band of input signalfrequencies in an extremely short time interval.

An additional object is to provide a logical decision element having avery short response time and producing signal gain.

Another object is to provide means for producing a stream of electronsand for gating the same during an extremely short time interval.

These and other objects of the present invention, as will appear from areading of the following specification, are accomplished in a preferredembodiment by the provision of a composite microwave tube structureadapted to receive two microwave input signals and operative to producean output microwave signal upon the simultaneous conditions that one ofthe input signals is present and the other is not. The compositemicrowave structure essentially comprises three distinct signal handlingregions connected in cascade. In the first of the regions, means areprovided for producing an electron beam and for accomplishinginteraction between said beam and one of said input signals whenpresent. The second region includes a device for selectively translatingto the third region the beam at the output of the first region dependingon whether said interaction has taken place. The beam is passed onlywhere no interaction occurred; otherwise, the beam is blocked. The thirdregion performs the function of selectively amplifying the second ofsaid input signals in the sole event that an electron beam is present atthe output of the second region; said second of the input signals isattenuated in the absence of such beam. In short, the second inputmicrowave signal is amplified only when there is no first inputmicrowave signal. The overall function is that of a decision elementwhich ice 2 performs the logical operation A-not, B, conventionallysymbolized by the notation KB.

A plurality of means are available for accomplishing interaction betweenthe first input microwave signal and the electron beam and, separately,for selectively translating the beam. For example, the interaction maybe such as to produce longitudinal velocity modulation of the electronbeam in the presence of the first input signal. In this case, thecriterion for selective translation of the beam is the averagelongitudinal velocity of the beam resulting from the interaction.Alternatively, the interaction between the first signal and the electronbeam may produce transverse deflection of the beam. The correspondingbasis for selective translation then is the deviation of the beam fromthe path that would be traversed by the beam in the absence of the firstsignal.

For a more complete understanding of the present invention referenceshould be had to the following specification and to the sole FIGUREwhich is a cut-away sectional view of a preferred embodiment.

The composite microwave tube structure of the figure essentiallycomprises three distinct signal handling regions respectivelyrepresented by the letters A, B and C. Region A includes conventionaltraveling Wave tube amplifier 4 whose Well known broad bandcharacteristic is particularly advantageous for responding to inputmicrowave pulses of extremely short time duration. The e ectron beam fortube 4 is produced by electron gun 3. Only focusing electrode 1 andaccelerating anode 2 of electron gun 3 of tube 4 are shown for the sakeof simplicity. The electron beam generated by gun 3 travels to the rightaxially through helix 5 in a conventional manner. The electron beam isfocused by the steady magnetic field generated by electromagnet coil 6.The microwave signal input to tube 4 is applied via coaxial line 7 whosecenter conductor 8 is directly connected to the input end of helix 5.

As is well understood, when the phase velocity of the electromagneticmicrowave signal traveling along helix 5 is made nearly the samemagnitude as the velocity of the electrons passing axially through thehelix, interaction between the traveling wave and the electron beamtakes place. The interaction is such to produce longitudinal modulationof the beam within helix 5 and amplification of the traveling wave. Theconsequent amplification of the traveling wave is of no particularsignificance to the present invention. For this reason, after theamplified traveling wave is coupled out at the end of helix 5 by coaxialline 9 it may be dissipated, if desired. Termination 10 is provided forsuch a purpose.

The amplification of the traveling wave results in the extraction ofkinetic energy from the beam. Thus, in addition to producinglongitudinal velocity modulation of the beam, the interaction alsoproduces a retardation of the average velocity of the beam flowingaxially through helix 5. Maximum velocity is imparted to the electronbeam in the absence of interaction, i.e., in the absence of an appliedinput microwave signal. Because of the broad band characteristic of tube4, the average velocity of the electron beam can be controlledessentially instantaneously by the application to axial line 7 ofmicrowave pulses of extremely short time duration even of the order ofone millimicrosecond.

The function of region B of the composite microwave tube is toselectively translate the beam at the output of tube 4 to the input ofthe apparatus of region C only in the case where no interaction hasoccurred between the electron beam and traveling wave within tube 4. Theapparatus of region B comprises an electron beam velocity sorter 11which transmits electrons having velocities above a predeterminedminimum value while rejecting electrons Patented Mar. 6, 1962.

having velocities below said certain value. As previously described,maximum beam velocity at the output of tube 4 occurs in the absence ofan input signal in coaxial line 7. The function of the velocity sorter11, therefore, is to pass such maximum velocity electrons and to blockthe passage of all others.

Velocity sorter 11 includes three apertured discs 12, 13 and 14connected in tandem along the axis of the electron beam. All three discsconsist of electrically conductive material. Discs 12 and 14 areelectrically connected to shell 15 which encases the over-all compositemicrowave tube. Disc 13 is supported within shell 15 by a circular discof dielectric material 16 which electrically insulates metallic disc 13from shell 15. Disc 13 is maintained at a negative potential relative togrounded shell 15 by means of a DC. source generally represented bynumeral 17.

An electrostatic field is generated between discs 12 and 13 whichretards the motion of the electron beam axially emerging from the outputend of helix 5. An equal but opposite electrostatic field is generatedbetween discs 13 and 14 which acts to accelerate any electrons whichsucceed in penetrating the aperture of central disc 13. The negativepotential applied by source 17 to central disc 13 is selected so as topermit only the passage of beam electrons having maximum velocity at theoutput of helix 5. This maximum velocity, as previously discussed,occurs only in the absence of interaction between the electron beam andthe traveling wave within tube 4. This, in turn, occurs only in theabsence of an input microwave signal at coaxial line 7. The negativepotential applied to disc 13 is sufficient to repel substantially allelectrons traveling at lesser velocities which lesser velocities resultfrom interaction, i.e., from the presence of an input microwave signalapplied via coaxial line 7.

Assuming that no input microwave signal is applied to tube 4, theelectrons emerging through the aperture of disc 13 are accelerated backto substantially the same interaction velocity which exists at theoutput end of tube 4. The accelerated electrons are applied to the inputend of the apparatus of region C.

Region C comprises a second traveling wave tube 18 essentially identicalto traveling wave tube 4. A second microwave signal is applied to helix19 via coaxial line 20. The accelerated electrons passing through disc14 are maintained in a focused beam for axial passage through helix 19by the steady magnetic field generated by electromagnet coil 21. Theelectron beam exiting from the helix 19 of tube 18 is captured in aconventional manner by means of collector 22. Collector 22 is aperturedofii the axis of helix 19 to permit the output of helix 19 to be coupledto the inner conductor 23 of an output coaxial line (not shown). In thepresence of an electron beam flowing through helix 19, conventionalinteraction takes place between said electron beam and the microwavesignal applied via coaxial line 20 whereby said microwave signal isamplified.

In operation, the composite microwave tube structure of the sole figureis adapted to receive two microwave input signals at 7 and 20 and isoperative to produce an output microwave signal (coupled out by thecoaxial line including center conductor 23) upon the simultaneoussatisfaction of the two conditions that a microwave signal is present at20 and that no microwave signal is present at 7.

In the absence of a microwave signal at coaxial line 7, no

interaction takes place within tube 4 and maximum axial velocity isimparted to the electron beam emerging at the output end of helix 5.Velocity sorter 11 permits such maximum velocity electrons to escapethrough aperture 13 and, after acceleration, into the input end of helix19 of tube 18. Upon the further condition that a microwave signal isapplied via coaxial line 20, the microwave signal is amplified and iscoupled out by the output coaxial line which includes center conductor23. Thus, the presence of a signal at the output coaxial line isindicative of the presence of the signal on input coaxial line 20 andthe absence of a signal on input coaxial line 7. The over-all functionis that of a decision element which performs the logical operationA-not, B.

It will be seen that the composite microwave tube is a coincidencedevice by nature. Therefore, the duration of the output microwave signalis commensurate with the shorter of the durations of the two appliedinput signals. For example, the same millimicrosecond output microwavesignal will be produced upon the application of a one millimicrosecondsignal via coaxial line 20 in the continuous absence of a signal oncoaxial line 7 as will be produced upon the application of a continuousmicrowave signal via coaxial line 20 and a discretely discontinuousmicrowave signal on coaxial line 7 wherein the duration of thediscontinuity (absence of signal) is one millimicrosecond.

An illustrative device for the generation of microwave pulses havingdurations of the order of a millimicrosecond is disclosed in the articleThe Regenerative Pulse Generator by C. C. Cutler published in theFebruary 1955 Proceedings of the IRE, volume 43, page 140. Discretelydiscontinuous microwave signals having a discontinuity (signal absence)duration of the same order may be produced by employing the generator ofthe aforementioned publication in combination with the compositemicrowave tube of the present invention. In this case, the generatedmillimicrosecond pulses of microwave energy would be applied to coaxialline 7 while a continuous microwave signal is applied to coaxial line20. There would thus be produced a discontinuous output microwave signalhaving a discontinuity duration equal to that of the pulse applied bycoaxial line 7, namely, of the order of a millimicrosecond.

Although longitudinal velocity modulation is produced in input region Aof the preferred embodiment, the present invention contemplates the useof a broad band microwave device wherein transverse deflection ratherthan longitudinal velocity modulation of the electron beam is producedas a result of interaction. Microwave means for the transversedeflection of an electron beam are known in the traveling wave cathoderay tube art and are described, for example, in A High-SensibilityCathode- Ray Tube for Millimicrosecond Transients by K. J. Germeshausenet al. in the April 1957 IRE Transactions on Electron Devices, page 152.In this case, it will be necessary to replace velocity sorter 11 by ananalogous discriminator adapted to such transverse beam deflection. Asuitable discriminator would be an axially apertured metallic platewhich would permit the passage only of an undeflected beam(corresponding to no interaction in region A) while blocking a deflectedbeam (resulting from interaction in region A). By locating the apertureof the plate away from the undefiected beam axis, the logic of thedevice could be modified. That is, only the deflected beam would bepassed to region C whereupon an output microwave signal would beproduced in the simultaneous presence of two input microwave signals.The logical function thus performed could be represented by the notationAB.

While the invention has been described in its preferred embodiments, itis understood that the words which have been used are words ofdescription rather than of limitation and that changes within thepurview of the appended claims may be made without departing from thetrue scope and spirit of the invention in its broader aspects.

What is claimed is:

1. A composite microwave tube device having first, second and thirdsignal handling regions connected in cascade; said first regionincluding means for generating an electron beam, means coupled to saidbeam generating means for producing interaction between said electronbeam and a first traveling wave of microwave energy if present, andmeans for applying said first traveling wave of microwave energy to saidmeans for producing interaction, whereby said electron beam is modifiedonly in the event of interaction; said second region including means forselectively translating from said first to said third region apredetermined one of said electron beam and said modified electron beam;the third region comprising means adapted to receive a second travelingwave of microwave energy and for effecting interaction between saidsecond traveling wave of microwave energy and the selectively translatedone of said electron beam and said modified electron beam if present,whereby said second traveling wave of microwave energy is amplified inthe presence of said selectively translated electron beam, means forapplying said second traveling wave of microwave energy to thelast-named means, means coupled intermediate said first and thirdregions for preventing the application of said first traveling wave ofmicrowave energy to said third region, and means for coupling out saidamplified traveling wave of microwave energy.

2. A composite microwave tube device having first, second and thirdsignal handling regions connected in cascade; said first regionincluding means for generating an electron beam, means coupled to saidbeam generating means for producing interaction between said electronbeam and a first traveling wave of microwave energy if present, andmeans for applying said first traveling wave of microwave energy to saidmeans for producing interaction, whereby said electron beam is modifiedonly in the event of interaction; said second region including means forselectively translating from said first to said third region only saidmodified electron beam; the third region comprising means adapted toreceive a second traveling wave of microwave energy and for efiectinginteraction between said second traveling wave of microwave energy andthe selectively translated modified electron beam if present, wherebysaid second traveling wave of microwave energy is amplified in thepresence of said selectively translated modified electron beam, meansfor applying said second traveling wave of microwave energy to thelast-named means, means coupled intermediate said first and thirdregions for preventing the application of said first traveling wave ofmicrowave energy to said third region, and means for coupling out saidamplified traveling wave of microwave energy.

3. A gated traveling wave tube amplifier comprising means for generatingan electron beam, means for directing said electron beam along an axis,firs-t means connected to said beam generating means for producinglongitudinal velocity modulation of said electron beam in response to afirst input microwave signal, said electron beam when modulated havingan average velocity which is less than a predetermined value, velocitysorting means connected to said first means for selectively translatingsaid electron beam only when the average velocity thereof exceeds saidpredetermined value; said velocity sorting means comprising first,second and third centrally apertured metallic discs disposed coaxiallyalong said axis, and means for maintaining said apertured discs atpotentials whereby said electron beam is decelerated in the regionbetween said first and second discs and accelerated in the regionbetween said second and third discs; second means coupled to saidvelocity sorting means for producing interaction between the selectivelytranslated electron beam and a second input micro-wave signal wherebysaid second input microwave signal is amplified in the presence of saidselectively translated electron beam, and means for coupling out theamplified microwave signal.

References Cited in the file of this patent UNITED STATES PATENTS2,250,511 Varian et al. July 29, 1941 2,584,597 Landauer Feb. 5, 19522,653,270 Kompfner Sept. 22, 1953 2,790,927 Pierce Apr. 30, 19572,801,361 Pierce July 30, 1957 2,899,598 Ginzton Aug. 11, 1959 2,954,553Gruenberg Sept. 27, 1960 FOREIGN PATENTS 1,141,687 France Mar. 18, 1957815,063 Great Britain June 17, 1959

